Any way to reduce bind9 memory footprint?

You can take a look into options like:

• datasize [bytes]
• max-cache-size [bytes]
• tcp-clients [number]
• recursive-clients [number]

These are all global options that may actually cause your server to stop responding once hitting the caps, but will limit the memory used.

For a real world example, with a setting of "max-cache-size 1M" my BIND install is using just about 30-35MB of memory (uptime 2 weeks, authoritative for 9 zones, light traffic).